1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device in which a surface of a semiconductor body is provided with a first insulating layer having a dielectric thickness which is homogeneous throughout the surface, on which a first conductor pattern of polycrystalline silicon is provided, on which first conductor pattern a second insulating layer is formed by oxidation of said pattern in such manner that the dielectric thickness of the first insulating layer remains approximately constant, after which a second conductor pattern is provided on and beside the second insulating layer.
"Approximately constant" is to be understood to mean herein that, as a result of treatments in connection with the oxidation of the first conductor pattern, the dielectric thickness at the area of the first insulating layer may deviate at most .+-.50% from the original value.
2. Description of the Prior Art
Such a method is disclosed in U.S. Pat. No. 4,077,112.
In this method a silicon semiconductor body is provided with a first insulating layer which consists of a silicon dioxide layer and a silicon nitride layer.
After providing the first conductor pattern and forming the second insulating layer the silicon nitride layer beside the first conductor pattern is removed and the thickness of the silicon dioxide layer beside the first conductor pattern is increased by oxidation so that the dielectric thickness at the area of the first insulating layer remains constant.
It has been found that during oxidation of a conductor pattern provided on a first insulating layer the resulting second insulating layer may have a rounded shape at the edges of the pattern near the first insulating layer so that spaces are formed below the edges of the second insulating layer.
This results in a number of problems which can detrimentally influence the desired operation of the semiconductor device to be manufactured.
If, for example, the second conductor pattern consists of polycrystalline silicon, the spaces between the insulating layers are also filled when said material is provided in the usual manners.
During the formation of the second conductor pattern from the provided material the polycrystalline silicon is often not removed from the spaces. As a result of this, parts of the second conductor pattern which overlap parts of the first conductor pattern can be short-circuited via a polycrystalline wire formed in the spaces between the insulating layers.
Indeed, when the polycrystalline silicon is removed from the spaces, the possibility exists that upon providing a subsequent insulating layer, for example, of silicon oxide, a bad step coating is obtained at the area of the spaces.
A bad step coating is therefore obtained if a third conductor pattern, for example of aluminium, is provided on the said subsequent insulating layer. This third pattern may then even show interruptions.
Furthermore, the distance between two overlapping parts of polysilicon conductor patterns at the area of the spaces is minimum and an increase in density of field lines takes place there due to the tapered nature of the spaces so that the breakdown voltage between the overlapping parts is decreased.
If the second conductor pattern consists of aluminium, the spaces between the insulating layers during its provision are not filled and the step coating at the area of said spaces is bad so that the second conductor pattern may show interruptions.
At the area where the second conductor pattern is not present, a subsequent insulating layer, if any, and a third conductor pattern above the spaces may show serious defects.